Method for packaging contamination vulnerable articles and package therefore

ABSTRACT

A package for the transportation of contamination vulnerable articles is provided, comprising a closeable plastic container which is loaded with the respective articles, a first bag made from plastic surrounding said container, and a second bag made from plastic wrapping said first bag, wherein said first bag is provided with a valve-filter arrangement in order to allow a controlled air stream into said first bag when opening said valve-filter arrangement.

BACKGROUND OF THE INVENTION

The present invention relates in general to packages for contaminationvulnerable articles. More specifically the invention relates to suchpackages for the transportation of semiconductor wafers. The inventionalso pertains to a transportation device for such contaminationvulnerable articles.

Semiconductor wafers are generally dispatched from the manufacturer tothe purchaser's premises. During transportation, long distances oftenhave to be covered and the means of transport may have to be changedfrequently. Therefore, there is a considerable risk that the sensitivesemiconductor wafers may be damaged. Even without any visible damagecaused by scratches or fracturing, impurities may have a considerableadverse effect on the semiconductor wafers or even make them un-useablefor the desired purpose, namely the fabrication of electroniccomponents.

It had been found that after transportation wafer substrates showsignificantly higher particle contamination values as compared to thelevel right after fabrication. This fact can be easily explained via thefollowing mechanism:

Usually, wafer substrates are delivered in transport boxes, known asFront Opening Shipping Box (FOSB), each containing 25 wafers. The boxesare double bagged to avoid particle contamination. The bags areindividually evacuated during sealing in order to prevent burstingduring, e.g., aircraft transportation. Examples of such methods can befound, e.g., in US 2002/023413 A1, JP 54043461 A2, JP 60167414 A2 and JP60167415 A2.

When the bags are opened at the customer's premises (usually by a simplecut with a knife), the pressure gradient between the exterior of the bagand the interior of the bag causes particles residing at the bag surfaceto be sucked in. A fraction of these particles finally ends up on thewafer box itself, and some of those consequently also on the wafersthrough the seal and on the wafers once the box is opened.

Additional box cleaning procedures will not completely cure this problemsince particles present in the sealed gap between the box body and thelid of the FOSB will not be cleaned off but drop into the boxes interiorwhen the door is removed.

U.S. Pat. No. 6,131,739 discloses a shock-absorbing package for aplurality of containers holding semiconductor wafers, consisting of twohalf-shells of foamed plastic configured with recesses into which thecontainers are placed in a positive-fitting manner. A container of theFOSB type is described, for example, in U.S. Pat. No. 6,581,264. Ashock-absorbing package of this type is suitable for reducing the riskof mechanical damage to the semiconductor wafers during transport.

In U.S. Pat. No. 6,155,027 there is described an encased and evacuatedcontainer for semiconductor wafers, which should protect the wafers fromcontaminating particles during transport.

U.S. Pat. No. 6,119,865 discloses a container for stacking of framedwafers comprising means for binding moisture.

In U.S. 2002/0153526 A1, there is described an encased container forwafers arranged between shock-absorbing elements in an outer packaging.

Finally, DE 10 2004 019 664 B4 and DE 10 2004 063 912 A1 disclose aready-for-dispatch package for semiconductor wafers and a method for theready-for-dispatch packaging of semiconductor wafers, respectively,comprising a) a closeable plastic container which is loaded with thesemiconductor wafers and has a lid and a body, a seal between the lidand the body and a particle filter which is integrated with thecontainer and allows exchange of gas between the interior space of thecontainer and the external environment of the container; b) a firstsheath made from plastic, which surrounds the container and restsclosely against the container with the aid of reduced pressure; c) ameans for binding moisture; d) a second sheath made from coated plastic,with a coating which blocks the passage of moisture and rests closelyagainst the first sheath and against the container with the aid ofreduced pressure; e) a shock-absorbing structure which embeds thesheathed container in a positive-fitting manner; and f) an outerpackaging which surrounds the double-sheathed and embedded container ina positive-fitting manner.

However, these containers and packages do not solve the problem that thesensitive wafers are damaged by contaminating particles when opening thebags at the customer's premises. Accordingly, there is still a need forpackages that do overcome this disadvantage.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor packaging contamination vulnerable articles that overcomes the abovementioned disadvantage.

It is a further object of the present invention to provide a package foruse in the above method.

These and other objects and advantages are achieved by the methoddisclosed in claim 1 and the transportation device disclosed in claim 8.

Advantageous embodiments of the invention are disclosed in the dependentclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in more detail below in connection withthe accompanying drawings, in which

FIG. 1 schematically shows one particular embodiment of the invention;

FIG. 2 depicts a well-shut tubing according to the invention;

FIGS. 3A and 3B depict a filter element according to the invention; and

FIGS. 4A and 4B are flow charts comparing the process of handling thepackaged wafers according to the state of the art as compared to theinventive process.

DETAILED DESCRIPTION OF THE INVENTION

First of all, it has to be mentioned that the present invention is notrestricted to wafers, but can be used with any articles that arecontamination vulnerable and thus need protection during shipment.However, in the following, the invention is described in more detail inview of semiconductor wafers as an example.

As has been described before, the boxes containing the wafers aredouble-bagged to avoid particle contamination. According to theinvention, the bags are modified in such a way that the first bag, i.e.,the bag wherein the wafer box is packed (or, in the following called theinner bag), carries a valve as well as a filter element attachedthereto. In a special embodiment, the second bag, i.e., the bag wrappedaround the first bag (or, in the following called the outer bag) isprovided with such a valve and filter element as well.

FIG. 1 schematically shows one particular embodiment of the invention.It has to be mentioned that the skilled worker will readily think ofother embodiments to realize such a valve-filter. Such designs areusually cost-driven and FIG. 1 shows an economically priced embodiment.In a corner portion 2 of the inner standard vacuum sealing bag 4, avalve 6 is arranged. This valve can also be arranged elsewhere in thebag, however, arranging it in a corner portion is advantageous becauseit is easier to attach and easier to access in order to open the bag.The valve 6, advantageously formed of one single piece, consists of anelongated flexible plastic tubing part 8 that is mounted to the sealingbag 4 by welding or glueing or is directly integrated into thepackaging. The tubing part 8 consists of a lower part 10 arranged so asto extend into the bag 4, and an upper part 12 protruding from the bag.The upper part 12 is closed at its top. According to FIG. 2, theflexible plastic tubing 8 (also called weld shut tubing) consists of aplastic tube 14 closed on one side, i.e., having a U-shape. Welded intosaid plastic tube is a filter element 16, shown in detail in FIGS. 3Aand 3B. This filter element may be a commercially available filterelement such as, e.g., an Ultra Low Penetration Air (ULPA) filter sheet.The filter holder 18, wherein the filter sheet 20 is arranged, may havea design as shown in FIG. 3B. It may consist of a plastic tube 22showing an integrated holder 24 for the filter sheet 20.

The first bag gets removed through pressure release by cutting off thesealed end of the filter valve along line 26 (cf. FIG. 1), thus allowinga controlled air stream into the second bag. The filter secures thatonly particle free air is released from the evacuated bag. The sameprocedure is used to open the inner bag. In case also the inner bag isprovided with the inventive valve, the desired effect is increased.

The plastic tubing 8 in combination with the filter element 16, builtinto the bag 4, has the function of a valve filtering the air fromparticles. The filter pore size determines the particle limit filtered,which should satisfy regular class 1 clean room conditions. Afteropening the weld-shut, the pressure release goes fairly slow due to thefilter resistance.

As has already been described above, in the old packaging process, theFOSB is packed into two bags, one after the other, and each bag getsevacuated to achieve shipment protection.

In the new, inventive method, the wafers are loaded into the FOSB fortransportation in the packaging area. The FOSB then gets closed and isput into the first bag being provided with a filter wave included in acorner portion of the bag. The bag then gets evacuated to protect thebox during shipment. For additional protection a second bag is used thatmay also include the filter-valve. The second bag is evacuated as wellto additionally protect the box during shipment.

FIGS. 4A and 4B depict flowcharts comparing the old (FIG. 4A) and thenew (FIG. 4B) packaging process flow. The typical problem is that aftersorting from an FOSB into a Front Opening Unified Pad (FOUP) at thecustomer's premises, at least the wafers in the first and the last slotof the containers show increased particle contamination. This is prettymuch a common problem in industry caused, as has already been explained,by the pressure difference and the leaky seals of the boxes. The typicalaction to resolve this problem up to now is that the wafers have to seewet cleaning, which is an additional process step with remaining risk,due to handling and treatment.

The controlled opening by cutting off the valves according to theinvention causes slow pressure release in the bag(s). This preventsparticles which are located on the outer bag's surface from being suckedonto the inner bag or the FOSB surface, respectively. From the boxsurface the particles reach into the box through the seals, which, inthe prior art, are not designed to stay the rapid pressure difference.Thus, the controlled opening of the bag(s), using the valves including afilter, has the positive effect that the wet cleaning of the wafers canbe eliminated.

The advantages of the inventive device and method are as follows:

-   -   No additional inspection, rework and further cleaning required.    -   Improvement of yield and substrate phase in the process.    -   Prevention of particle contamination, triggered through bag        opening, the filter pore size depending on the cleanliness        requirements.    -   very simple application, only air filters have to be added to        the bag(s).

1. A package for the transportation of contamination vulnerablearticles, comprising a closeable plastic container which is loaded withthe respective articles, a first bag (4) made from plastic surroundingsaid container, and a second bag made from plastic wrapping said firstbag (4), wherein said first bag (4) is provided with a valve-filterarrangement (6, 16) in order to allow a controlled air stream into saidfirst bag (4) when opening said valve-filter arrangement (6, 16).
 2. Thepackage according to claim 1, wherein said contamination vulnerablearticles are semiconductor wafers.
 3. The package according to claim 1,wherein said valve-filter arrangement (6, 16) is mounted into a cornerportion (2) of said bag (4).
 4. The package according to claim 3,wherein said mounting is accomplished by welding or heat glueing.
 5. Thepackage according to claim 3, wherein said valve-filter arrangement (6,16) is directly integrated into the packaging.
 6. The package accordingto claim 1, wherein said valve-filter arrangement (6, 16) consists of aplastic tube (8) and a filter element (16) welded thereinto.
 7. Thepackage according to claim 1, wherein the second bag is additionallyprovided with said valve-filter arrangement (6, 16).
 8. The packageaccording to claim 1, wherein said plastic container is a Front OpeningShipping Box (FOSB).
 9. The package according to claim 1, wherein saidtubing part (8) consists of a lower part (10) and a sealed upper part(12) closed at its top.
 10. The package according to claim 1, whereinsaid filter element (16) consists of a filter holder (18) and a filtersheet (20).
 11. The package according to claim 10, wherein said filterholder (18) is a U-shaped plastic tube (14).
 12. A method for packagingcontamination vulnerable articles, comprising the steps of loading saidarticles into a closeable plastic container, surrounding said containerwith a first plastic bag (4), and surrounding said container and saidfirst plastic bag with a second plastic bag, wherein said first plasticbag (4) is provided with a valve-filter arrangement (6, 16) in order toallow a controlled air stream into said first bag (4) when opening saidvalve-filter arrangement (6, 16).
 13. The method according to claim 12,wherein said contamination vulnerable articles are semiconductor wafers.14. The method according to claim 12, wherein said second bag isadditionally provided with said valve-filter arrangement (6, 16). 15.The method according to claim 12, wherein said first bag (4) is openedby cutting off said sealed upper part (12).